This invention relates generally to circuit board assemblies. In particular, the invention relates to assemblies of circuit boards and optical transceiver modules.
Infrared transceivers modules are often incorporated into electronic devices to enable bi-directional wireless communication with other electronic devices. For example, it is known for a portable digital assistant (PDA) to communicate with a laptop computer, a printer, or another PDA via a standard Infrared Data Association (IrDA) link. Similarly, IR transceivers are becoming increasingly popular for use in hand-portable telephones, enabling telephone users to swap stored numbers, play wirelessly-linked games, or wirelessly link their telephones to IR-enabled accessories.
The advantages of using an IR link over standard electrical connectors are numerous and well documented. These advantages include: 1) greater alignment tolerance; 2) the ability to hermetically seal the data interface; 3) no cables susceptible to RF interference; and 4) no electro-magnetic compatibility (EMC) issues.
An IR transceiver module typically comprises a light emitting diode (LED) and a photodiode, packaged together with appropriate supporting circuitry to form a self-contained unit. Electrical terminals are exposed on the outside of the package to enable the module to be electrically coupled to external circuitry.
By combining the various components of an IR transceiver into a single package or module, the size or form-factor of the transceiver system can be considerably reduced. Furthermore, the modules tend to be more durable and often consume less power than equivalent transceivers consisting of discrete components.
When an IR link or communication channel is created between two IR transceiver modules, the LED in the first transceiver optically couples with the photodiode in the second transceiver, and the LED in the second transceiver optically couples with the photodiode in the first transceiver. Although the transceivers typically operate in the infrared optical frequency band it is equally possible for other optical frequency bands to be used in forming the communication channel.
FIG. 1 shows a prior art hand-portable telephone 100, such as the Model 6110 cellular telephone available from Nokia Mobile Phones Oy, Finland, which incorporates a known IR transceiver module (not shown). The telephone includes a standard keypad 110, a display 120, and an antenna 130. The telephone housing 140 encloses circuitry including a IR transceiver module positioned adjacent an IR transparent window 150. The window is transparent to IR radiation enabling the IR transceiver module to communicate optically with other devices outside the housing 140.
FIG. 2 is a more detailed view of the internal circuitry of the hand-portable telephone of FIG. 1, showing the IR transceiver module 200 mounted on an end portion of a main printed circuit board (PCB) 250. The transceiver module 200 is formed with a first molded lens shape 210 over the LED and a second molded lens shape 220 over the photodiode. Leads 230 provide mounting supports and electrical interconnections between the IR transceiver 200 and the printed circuit board 250. A typical length xe2x80x9cLxe2x80x9d for the IR transceiver body is approximately 10 mm, a typical depth xe2x80x9cDxe2x80x9d is 5 mm, and a typical height xe2x80x9cHxe2x80x9d is 4 mm. A typical thickness xe2x80x9cTxe2x80x9d for the printed circuit board 250 is 1 mm.
Consumer pressure is driving electronic device manufacturers such as radio telephone manufacturers to produce ever slimmer products. One way to help reduce the thickness of these products is to minimising the thickness of printed circuit boards contained in the products. Components mounted on the printed circuit boards contribute to the overall circuit board thickness. Therefore, by reducing the height of components on the circuit board, the circuit board thickness may be reduced which in turn can enable slimmer products to be manufactured. Excessive height above a circuit board can thus be a problem for components.
One solution for reducing the height of components on a circuit board is to simply use smaller components. Components are now available which when mounted directly on a circuit board stand less than 1 mm from the board surface. However, for components with optical lenses such as infrared transceiver modules, the module height is limited by the diameter of the lens. The lenses must be of a minimum size to ensure adequate performance of the IR transceiver and to satisfy legislated eye safety requirements (lenses smaller than the minimum size can concentrate light emitted from the transceiver to dangerous levels). Some manufacturers have overcome the lens size limitation by cutting off small portions from each lens. This approach again leads to a degradation in the performance of the IR transceiver. The smallest IR transceiver module currently available has a height of 2.5 mm.
Another solution for reducing the height of components on a circuit board is disclosed in U.S. Pat. No. 5,506,445, assigned to Hewlett-Packard Company, USA. FIGS. 3 and 4 illustrate this solution which involves mounting a leadframe IR transceiver adjacent an end surface of a printed circuit board by means of a series of shaped leads 230. An alternative lead arrangement adopted by one manufacturer, Vishay Company, USA, is shown in FIG. 5. This solution has drawbacks. Firstly, the leads on these packages need to be long enough to enable them to correctly attach to the circuit board. However, long leads cause co-planarity problems which in turn causes a high percentage of products to fail during manufacture. Secondly, the complex arrangement of the leads makes lead trimming difficult and expensive to achieve during manufacture. Thirdly, the lack of a surface on which the IR transceiver body is supported results in an inherently unstable device assembly. Altemating motion stresses are concentrated directly on the solder joints coupling the IR transceiver module to the printed circuit board. An additional problem which the applicant has found In practice is that the IR transceiver does not lend itself to automated assembly. The complex alignment and a lack of pick and place surface mean that manual assembly is necessary for this type of product.
The foregoing illustrates that there is need for a low profile optical transceiver which overcomes the drawbacks associated with the prior art.
The present invention provides a system for assembling a circuit board and an optical transceiver module, in which the optical transceiver module is mounted onto an additional substrate. The additional substrate allows the optical transceiver module to be placed within an open slot of the main circuit board, thus reducing the effective height of the module from the circuit board surface. Suitably, the additional substrate provides electrical interconnections between the optical transceiver module and the circuit board.
According to a first aspect, the present invention provides a circuit board assembly comprising; a planar circuit board having a major surface and a side surface, a planar substrate mounted on the major surface of the circuit board, an extended portion of the planar substrate extending beyond the side surface, and an optical transceiver module mounted on the extended portion of the substrate adjacent the side surface of the printed circuit board.
According to a second aspect, the present invention provides a circuit board assembly comprising; a planar circuit board having a major surface, and a side surface defining a recess, a planar substrate mounted on the major surface of the circuit board, an extended portion of the planar substrate extending over the recess, and an optical transceiver module mounted on the extended portion of the substrate so as to be disposed in the recess.
According to a third aspect, the present invention provides an optical transceiver module package for mounting on a planar circuit board having a major surface and a side surface, the major surface provided with electrical terminals, the optical transceiver module package comprising: a planar substrate for mounting on the major surface of the circuit board so that an extended portion of the planar substrate extends beyond the side surface, an optical transceiver module provided with electrical terminals and mounted on the extended portion of the substrate adjacent the side surface of the printed circuit board, and electrically conductive interconnects associated with the planar substrate for coupling the electrical terminals on the optical transceiver module with electrical terminals on the planar circuit board.
According to a fourth aspect, the present invention provides an optical transceiver module package for mounting on a planar circuit board having a major surface and at least one side surface defining a recess, the major surface provided with electrical terminals, the optical transceiver module package comprising: a planar substrate for mounting on the major surface of the circuit board so that an extended portion of the planar substrate extends over the recess, and an optical transceiver module provided with electrical terminals and mounted on the extended portion of the substrate so as to be disposed in the recess, and electrically conductive interconnects associated with the planar substrate for coupling the electrical terminals on the optical transceiver module with electrical terminals on the planar circuit board.
A circuit board assembly or optical transceiver module package in accordance with the invention has the advantage that the optical transceiver module is mounted on a planar substrate instead of the circuit board, which avoids the optical transceiver module protruding directly from the circuit board surface. Consequently, the effective height of the optical transceiver module can be reduced by at least the thickness of the circuit board, allowing the module to protrude or extend less from the from the circuit board surface. Thus, the overall thickness of the circuit board assembly can be reduced.
The optical transceiver module package which includes the planar substrate in accordance with the present invention also has the advantage that it can be assembled with the circuit board using a standard pick and place machine.
Suitably, the planar substrate provides a surface from which the pick and place machine can hold and manoeuver the optical transceiver module package.
In a preferred embodiment, the planar circuit board includes an end portion defining a recess in which the optical transceiver module is disposed In accordance with another aspect of the invention, a side surface of the circuit board may define the recess. This side surface may be a single continuous surface defining the recess or a multi-faceted surface made up of a two or more joined panels defining the recess.
Ideally, the planar substrate includes electrically conductive interconnects for coupling electrical terminals on the optical transceiver module with electrical terminals on the planar circuit board.
According to a fifth aspect, the present invention provides a method of manufacturing a circuit board assembly comprising: providing a planar substrate, mounting an optical transceiver module on a first portion of the planar substrate, and mounting a second portion of the planar substrate on a major surface of a circuit board such that the optical transceiver module is disposed adjacent a side surface of the planar circuit board.
A method in accordance with the invention has the advantage that it enables the optical transceiver module to be packaged together with the planar substrate for subsequent mounting on the planar circuit board, which in turn enables the optical transceiver module to be reliably packaged prior to mounting on the circuit board. The optical transceiver module package can be manufactured on a large scale, and each package can then be reliably mounted on the circuit board. Pick and place machines can be used advantageously to hold and manoeuver the optical transceiver module package during mounting on the circuit board.
In a preferred method in accordance with the invention, the planar substrate is separated from a relatively larger planar substrate using a singularising step.
Preferably, a multitude of planar substrates are singularised from the larger planar substrate, with each planar substrate including an optical transceiver module.